docs: def indent(self, space=4):
          '''Return an indented Newick string, just like ``nw_indent`` in Newick Utilities
  
          Args:
              ``space`` (``int``): The number of spaces a tab should equal
  
          Returns:
              ``str``: An indented Newick string
          '''
          if not isinstance(space,int):
              raise TypeError("space must be an int")
          if space < 0:
              raise ValueError("space must be a non-negative integer")
          space = ' '*space; o = []; l = 0
          for c in self.newick():
              if c == '(':
                  o.append('(\n'); l += 1; o.append(space*l)
              elif c == ')':
                  o.append('\n'); l -= 1; o.append(space*l); o.append(')')
              elif c == ',':
                  o.append(',\n'); o.append(space*l)
              else:
                  o.append(c)
          return ''.join(o)